Today, when a cell phone suffers fading with its primary antenna, it switches to a diversity antenna to avoid the spatial null causing weak reception by the primary antenna. This diversity antenna is connected to the receiver via a costly micro-coaxial cable, for which the industry is seeking an alternative solution that improves reception.
To reduce size and cost, cell phones use the primary antenna to both transmit and receive signals, although this exposes the receive chain to incursion by powerful transmit signals, causing cosite interference that disrupts reception. Anti-cosite devices used to prevent this, e.g. duplexed pairs of off-chip filters, switches and circulators, currently provide insufficient protection, clearly creating a need for an alternative solution. Accordingly, in light of the above, there exists a need for devices and methods for providing enhanced diversity reception and cosite cancellation.
The demand by cell phone users for higher data transfer rate (“speed”) is driving the evolution of wireless standards to include aggregation of multiple carriers at different frequencies, making rejection of self-interference (“blockers”) more challenging that can slow or disrupt data transfer. Added to this are the fixed frequency carrier selection filters used today, which comprise off-chip components that are driving the cost and size of cell phone front ends. Replacing off-chip filter banks with active circuits can save cost and space but would create noise and risk distortion caused by insufficient blocker mitigation, making existing active filters an unacceptable alternative to today's filter banks.
In light of this, we disclose active integrated circuits and methods for wideband tunable carrier aggregation (“CA”) filtering wherein channel selection filtering rejects out-of-band frequencies to mitigate blockers and other sources of OOB interference, and circuit noise within the channel or channels to enable enhanced carrier aggregated reception of wireless signals.